1. Field of the Invention
The invention relates to a method for diagnosing a short circuit of a capacitive actuator, in particular a piezoelectrically operated fuel injection valve of an internal combustion engine of a motor vehicle.
German Patent DE 196 52 801 C1 discloses a device for driving capacitive actuators, by which the actuators, of which each is connected in series with a selector switch constructed as a low-side switch, are charged one after another from the series circuit of a charging capacitor and a recharging capacitor.
It has emerged from the operation of such circuits that shorts of the negative--but also of the positive--actuator terminal to the frame can occur with such actuators. This fault (if not all actuators are short circuited in the case of a short circuit of a positive actuator terminal) has the effect that as every other actuator is driven the actuator short circuited to the frame is also always driven. These two actuators act relative to the drive circuit like one actuator with double the capacitance.
However, since the capacitance of an actuator can likewise vary by a factor of 2 in the permissible temperature range, this fault cannot be detected with the aid of simple voltage monitoring.